Investigating the Dielectric Properties of Various Embolic Agents at 915 MHz and 2.45 GHz

A 4.5 GHz Vector Network Analyzer and dielectric probe (N1501A, Keysight Technologies) were used to measure the dielectric properties of various embolic and contrast agents. All embolic agents were prepared following the manufacturer's instructions. Two different frequencies were studied during measurements, with one broad frequency sweep performed with the dielectric probe submerged in 2mm of the embolic or contrast agent. Dielectric real ε was analyzed at two range frequencies averaged adjacent to 915 MHz (range 856–991 MHz) and 2.45 GHz (range 2.39–2.52 GHz). Embolic agents tested in this study are as follows: Glue (3:1, lipiodol to histoacryl), Boston Scientific LC LUMI beads 70-150 µm, Obsidio, Varian Oncozene 40 µm, Oncozene 75 µm, Embospheres 250 µm, SIRTEX LAVA 18, and LAVA 34. Additionally, the dielectric properties of contrast agents Visipaque 320, Omnipaque 350, and Lipiodol were tested. 

Results: Mean ε at 915 MHz ranged from highest to lowest as follows: 1) LAVA 34, 48.3 ± 2.5, 2) LAVA 18, 43.4 ± 2.2, 3) Oncozene 75, 43.1 ± 2.3, 4) LUMI 70-150, 42.9 ± 2.2, 5) Oncozene 40, 42.8 ± 2.3, 6) Obsidio, 42.8 ± 2.3, 7) Glue, 42.7 ± 2.2, and 8) Embospheres, 42.7 ± 2.3. Contrast agents being Visapaque 43.0 ± 2.2, Lipiodol 43.0 ±  2.2 and Omnipaque 42.9 ± 2.4. Mean ε at 2.45 GHz as follows: 1) LUMI, 52.8 ± 1.2, 2) LAVA 34, 51.9 ± 1.3, 3) Oncozene 75, 51.1 ± 1.2, 4), Oncozene 40, 50.4 ± 1.4, 5) Embospheres 49.3 ± 1.4, 6) Glue 48.1 ± 1.4, 7) Obsidio, 47.4 ± 1.4, and 8) LAVA 18, 47.4 ± 1.4. Contrast agents ranked as follows: 1) Visipaque, 54.1 ± 1.2, 2) Omnipaque, 51.3  ± 1.0, and 3) Lipiodol, 47.7 ± 1.4. At 2.45 GHz, Visipaque demonstrated significantly higher ε than Omnipaque, 54.1 ± 1.2 vs 51.3 ± 1.0 (p < 0.05).

Conclusion: In this limited investigation of embolic and contrast agents, microspheres and Visipaque demonstrated higher permittivity at 2.45 GHz and LAVA 34 at 915 MHz. Using high and low ε embolic materials, further investigation in a MWA-TAE model may demonstrate if tissue properties change after embolization and impact MWA dimensions.